A method of handling a RRC connection resume procedure between a NAS layer and a RRC layer of a communication device, comprising the RRC layer entering a RRC idle mode and camping on a first cell of a network; the NAS layer in a NAS idle mode with suspend indication transmitting a first request message to the RRC layer to resume a RRC connection; the RRC layer starting a timer and transmitting a first RRC connection resume request message to the network, after receiving the first request message from the NAS layer; the RRC layer reselecting a second cell of the network, when the timer is running; and the RRC layer informing the NAS layer a failure of resuming the RRC connection with a first suspend indication.